1. Field of the Invention
The present invention generally relates to a permanent magnet rotating electric machine having rare earth permanent magnets for a field system, which are provided in a rotor, and more particularly, to a permanent magnet rotating electric machine that is mounted in, for example, a compressor of an air conditioner and that has concentrated wound stator windings.
2. Description of the Related Art
Generally adopted permanent magnet rotating electric machines of such a type employ permanent magnets of various shapes. For example, Domestic Republication of PCT International Publication No. WO97/31422 describes a permanent magnet rotating electric machine that comprises a stator, into which concentrated wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having permanent magnets inserted into a plurality of holes, which are formed in a rotor core and used for accommodating permanent magnets. Improvement in efficiency of this rotating electric machine, that is, what is called output enhancement is achieved by utilizing reluctance torque.
However, although the efficiency of this permanent magnet rotating electric machine is increased by effectively utilizing reluctance torque, no consideration is given to the efficiency of a system during driven by what is called a position sensorless inverter in the case of 120 degree energization.
In the case of this conventional machine, consideration is given only to the efficiency of a motor. Especially, in a rotor structure employing concentrated windings and utilizing reluctance torque, reluctance increases. Thus, the power factor of the rotating electric machine decreases for that, while electric current flowing therethrough increases. This increase in electric current results in reduction in inverter efficiency. Consequently, the system efficiency decreases, far from increasing.
The present invention is accomplished in view of the aforementioned problems.
Accordingly, an object of the present invention is to provide a permanent magnet rotating electric machine comprising a stator having concentrated windings and a rotor into which permanent magnets are embedded that can increase the system efficiency even when the rotating electric machine is driven by a position sensorless inverter in the case of 120 degree energization.
When a permanent magnet rotating electric machine is driven by a position sensorless inverter in the case of 120 degree energization, the performance of the machine is not determined only by the efficiency of the rotating electric machine or motor but is finally determined by the degree of the system efficiency defined as a product of the inverter efficiency and the efficiency of the rotating electric machine. For example, when the efficiency of the rotating electric machine is enhanced, an output current of the inverter increases in the case that the power factor of the motor decreases. Further, when the output current of the inverter increases, the voltage drop occurring in a control device of the inverter increases. Consequently, the inverter efficiency is reduced, so that the system efficiency is reduced, far from being enhanced. Thus, according to an aspect of the present invention, there is provided a permanent magnet rotating electric machine comprising a stator, into which concentrated wound armature windings are inserted in such a way as to surround a plurality of teeth formed in a stator core, and a rotor having rare earth permanent magnets inserted into a plurality of permanent magnet holes, which are formed in a rotor core and used for accommodating permanent magnets. In this rotating electric machine, the permanent magnets are each shaped like a convex xe2x80x9cVxe2x80x9d or xe2x80x9cUxe2x80x9d with respect to the shaft of the rotor. Moreover, the machine is configured so that the width of the interpole core at the outside-diameter side of the rotor is narrow, while the width of the interpole core at the inside-diameter side of the rotor is wide. Further, a ratio of width W1, which is narrowed at the outside-diameter side of the rotor, of an interpole core between the permanent magnets to width Xg of a gap between the stator core and the rotor core is set in such a manner as to satisfy the following condition: 10.8xe2x89xa6W1/Xgxe2x89xa613.2. Incidentally, the shaping of the permanent magnets like a convex xe2x80x9cVxe2x80x9d or xe2x80x9cUxe2x80x9d includes the shaping of the permanent magnets like an arc, and also includes the arranging of the permanent magnets like a letter xe2x80x9cVxe2x80x9d or xe2x80x9cUxe2x80x9d by combining the permanent magnets with each other.
Consequently, the present invention provides a permanent magnet rotating electric machine that enhances system efficiency when the reluctance thereof is set at an optimum value, and the machine is driven by a position sensorless inverter in the case of 120 degree energization.